Stem Cell Factor (SCF) is initially synthesized as membrane-bound forms of 248 or 220 amino acids, depending on alternative splicing of exon 6. The 248 amino acid form contains a proteolytic cleavage site encoded by exon 6, and it is cleaved from the cell to release an active soluble protein of 165 amino acid residues. Soluble SCF is glycosylated at both N-linked and O-linked sites. MMP-9 plays a physiological role in SCF release from the membrane, and this action plays a significant role in differentiating and mobilizing stem and progenitors cells from the bone marrow. SCF increases the proliferation of myeloid and lymphoid hematopoietic progenitors in bone marrow cultures. SCF/c-kit interaction in mast cells results in mast cell degranulation with release of mediators, such as histamine and inflammatory cytokines and chemokines. Also, activation of c-kit in dendritic cells regulates T helper cell differentiation and allergic asthma. In addition, SCF plays an important role in revascularization of ischemic limbs. Ischemia induces plasma elevation of SCF and thrombopoietin (TPO) and, in lower levels, GM-CSF and erythropoietin (EPO). SCF and TPO induce the release of CXCL12 from platelets, thereby increasing CXCL12 levels in plasma. This results in an extensive mobilization of CXCR4+VEGFR1+ cells (hemangiocytes), which accelerates revascularization of the ischemic limbs. SCF binds to its receptor kit that belongs to the type III tyrosine kinase family, whose members include receptors for M-CSF and PDGF.